Calibration and Multiple Reliability Assessments of a Scrum Machine Instrumented to Measure Force

Abstract

Featured Application: This research establishes the excellent reliability of S-type load cells used in instrumenting a scrum machine both after an extended (7 h) run time and over 6 months of use. Furthermore, we show excellent inter-trial reliability in human use. Researchers or coaches wishing to build a similar instrumented scrum machine could use these results as a benchmark and basis of comparison for their own machine. Coaches need reliable methods of quantifying rugby union scrum force performance in order to make data-driven decisions. The purpose of this study is to present the reliability of a replicable instrumented scrum machine. We performed 3 phases of deadweight calibration on 8 S-type load cells; during deadweight calibration, each load cell was loaded with ~20–200 kg. Phase 1 compared power sources (wall outlet vs. portable power station). Phase 2 tested the inter-session reliability of the load cells after 15, 30, 45, 60, and 420 min of run time. Phase 3 tested between-session reliability, comparing days 0, 1, 7, and 180. We also performed a phase of inter-trial reliability when humans pushed on the fully instrumented scrum machine. Fourteen collegiate rugby players performed four warm-up trials and then five 100%-effort trials; peak and average voltage during the push were compared between the 100%-effort trials. For all phases, statistical analyses show near-perfect reliability. Therefore, we conclude that our novel instrumented scrum machine is ready for in vivo data collection; other coaches or researchers could duplicate our methods to create their own reliable instrumented scrum machine.